A bearing is a machine element that constrains relative motion and reduces friction between moving parts to only the desired motion. A common class of bearings is roller bearings, which utilize balls or rolling elements to reduce friction. Another class of bearings operates without rolling members and is commonly referred to as plain or sliding bearings. Typically, these latter types of bearings rely on sliding movement (as opposed to rolling movement) and either an oil or a non-solid grease to lubricate or facilitate relative movement. One type of non-roller bearing uses oil which is continuously delivered to the surfaces of the bearing by a groove in one of the bearing surfaces. This type of bearing must operate at very high speeds (circa 10,000 rpm) so that the oil can create a hydrostatic film with sufficient force to prevent the load transfer surface and the bearing surfaces from making direct and often metal-to-metal contact. Direct contact leads to friction causing excessive heat and wear, as well as eventual seizure. Fully rotational, constant high speed is required to maintain the film. There is no mechanism for removing wear debris after it is generated in these types of bearings. Another type of non-roller prior art bearing relies on various viscosity greases to separate bearing surfaces from load transfer surfaces. The grease is applied to one of the bearing and load transfer surfaces. It has been established by bearing design tribologists that the maximum practical limit of PV (psi-sfm) of this type of bearing is approximately 50,000. PV is a measure of the performance capability of a sliding bearing.
P is a measure of pressure on the bearing's surface in pounds per square inch (psi), while V is a measure of the velocity of the bearing's surface in surface feet per minute (sfm). The product of the two, PV, is an indication of the performance capability of the bearing. The PV rating is sensitive to the composition of the materials of the contacting surfaces. Materials chosen for speed (high sfm), V, sacrifice their ability to support load capacity, P. Polymer materials (Polycarbonates, Acetyls, Nylon) whose PVs approximate 3,000, with a maximum P of 1,000 psi, fall into this class. Metals permit higher load carrying with PVs ranging from 20,000 to 50,000. Those with low coefficients of friction (i.e., higher lubricity) which include carbon graphite, bronze, tin-bronze, aluminum-bronze, are still limited by the maximum speed permitted, typically under 300 sfm. Conventional bearings fabricated with powdered metals typically operate in the 15,000 to 50,000 PV range. The best performance has been received by PM bearings referred to as porous iron and porous bronze, whose maximum PVs are 30,000 and 50,000, respectively. Generally, prior art bearings were not designed for removing debris between bearing surfaces and the load transfer surface. Rather, prior art bearings focused on the delivery of liquid lubricants to prevent surfaces from rubbing and generating wear particles.
Geometrically contoured bearings having improved load bearing capabilities and low maintenance attributes have been described in U.S. Pat. No. 8,105,172. The applications based on these teachings, however, are limited to one-piece bearings capable of being positioned on a shaft such as a universal joint cross.
Citation or identification of any reference in Section 2, or in any other section of this application, shall not be considered an admission that such reference is available as prior art to the present invention.